I. Field of the Invention
The invention generally relates to mobile telephone systems and in particular to satellite-based mobile telephone systems.
II. Description of the Related Art
Satellite-based mobile telecommunications systems are being developed that allow a mobile communications subscriber unit such as a mobile telephone to be used almost anywhere in the world. In one system, illustrated in FIG. 1, a fleet of low earth orbit satellites are used along with a set of ground base stations 10 called "gateways". Signals are transmitted from a subscriber unit 12 to satellites 14 (shown as a single satellite for ease of drawing), then relayed down to gateway 10 for routing to one of a set of local service providers, generally denoted 16, which provide an interconnection to local land line telephone networks such as a local Public Switched Telephone Network (PSTN) or to other communication networks operated by the service provider. Depending upon the nature of the communication, the signals are ultimately routed to, for example, a telephone connected to the land line network, or to a mobile telephone perhaps operating in another part of the world covered by a different gateway, or perhaps to computer system. The signals may encode voice communications such as telephone conversations or data communications such as, for example, facsimile transmissions, Internet connection signals, etc. The subscriber unit 12 may be a hand-held mobile telephone, a mobile telephone mounted in a boat, train or airplane, a laptop computer, a personal data assistant or any other suitable communications unit provided with the proper equipment for communicating with the gateway via the satellite fleet.
A single gateway may handle all telecommunications traffic within an area covering as much as 2000 by 3000 kilometers. FIG. 2 illustrates an exemplary coverage area 18 for a gateway 20 operating in Europe. As can be seen, the coverage area encompasses many countries. Each country typically has one or more service providers. Depending upon the implementation, each service provider may operate only within one country or perhaps only within a portion of one country. Such restrictions may result from physical limitations on the capability of the service provider system or from contractual or other legal constraints. For example, even though operationally capable of doing so, a service provider in France may not be contractually and/or legally allowed to handle mobile communications for a subscriber unit operating in Italy and vice versa. Hence, for subscriber units in France (such as exemplary unit 22), the gateway may need to route communications through a French service provider such as TE.SA.M.; whereas, for subscriber units in Italy, the gateway may need to route communications through an Italian service provider such as Finmeccanica. Further, as represented by arrow 24, subscriber units may move from one country to another. Even within a single country the gateway may need to selectively route communications to different service providers depending upon the location of the subscriber unit within the country. Moreover, the operator of the subscriber unit may be contractually obligated to use certain service providers in certain locations or may be subject to other legal constraints. In addition to any contractual limitations that may prevent telephone connections from the subscriber unit from being connected to particular service providers, the user of the subscriber unit may simply have certain preferences regarding which services provider to employ.
For these and other reasons, it may be desirable for the gateway to be able to reliably coordinate access among numerous service providers and among numerous mobile telephone users over a large geographical area. Previously, no adequate system has been developed for that purpose, particularly one which takes into account user preferences. Aspects of the invention of the grand-parent application cited above are directed toward providing such a system. Briefly, the grand-parent application describes a system for selecting a service provider based upon the location, speed, altitude or other position characteristic of a subscriber unit or upon service provider preferences provided by the subscriber unit, or both. Selection of the service provider is performed, for example, as part of set up operations for a telephone connection initiated by the subscriber unit or terminated at the subscriber unit, or as part of a system registration access procedure initiated by the subscriber unit.
Although the system of the grand-parent application is effective for selecting a service provider based upon the location or other position characteristic of the subscriber unit and thereby overcomes many of the problems described above, other problems remained when subscriber units are taken from one geographical area to another such as from one country to another or from one area code region to another.
For example, as typically implemented, the user of a subscriber unit is required to dial a long distance area code prefix to dial any telephone number, even if the user has carried the subscriber unit into the area code region of the number being called. Hence, even though the user is calling a telephone number that is a local telephone number in the region in which the user is currently located, the user is nevertheless required to dial the number as if it were a long distance call, complete with area code. Likewise, the user is typically required to dial both an international calling code and an area code prefix to dial any telephone number not in the home country of the user, even if the user has carried the subscriber unit into the country of the number being called. Such is particularly problematic for users operating subscriber units in portions of the world such as Europe wherein the user may frequently need to carry the subscriber unit from one country to another.
Occasionally, the user may forget these dialing restrictions and may dial a telephone number without the area code or international dialing code number expecting to be connected to a local number and instead, depending upon the implementation, being erroneously connected to the corresponding local number in the home area code or perhaps even in the home country of the user. Such can be a particularly significant problem if the local number being dialed is an emergency services telephone number such as "911" or a direct police, fire, or ambulance number. Indeed, in emergency situations the user is less likely to remember any dialing restrictions. Also, some subscriber units are provided with a special emergency telephone number button which automatically dials an emergency services number. Again, depending upon the implementation, the emergency number dialed may be that of an emergency services center back in the home area code or perhaps the home country of the user, rather than the intended local emergency services center. Operators of the telephone system may even be deemed liable for injuries or damages that might otherwise have been avoided if the emergency services telephone number had been directed to a local emergency services center.
Problems can also arise in connection with the need of a law enforcement agency to intercept or monitor telephone calls to or from certain subscriber units. The jurisdiction of the law enforcement agency to take such action may depend upon the location of the subscriber unit--particularly upon the county, state or country in which the subscriber unit is located. For example, the law enforcement agencies of a particular country may be allowed to intercept telephone calls to or from a subscriber unit while located within their borders but not within other countries borders. For satellite-based systems, wherein the subscriber unit may be taken from one country to another, it may no longer be certain whether the law enforcement agency has proper jurisdiction to intercept telephone calls to or from the subscriber unit.
For these and other reasons, it may be desirable for a gateway or other mobile communications system to be able to direct, intercept or otherwise process telephone calls to and from subscriber units based upon the location of the subscriber unit. Aspects of the invention of the parent application were directed toward that end. Briefly, the parent application described a mobile communications system, such as the gateway system of a satellite communications system, configured to process telephone call connection requests from a mobile subscriber unit based, in part, upon the location of the subscriber unit. The system is, in one example, configured to parse telephone numbers received from the subscriber unit based upon the parsing scheme of the locality in which the subscriber unit is located at the time the telephone call is placed. Thus, if the user of the subscriber unit dials a local number, the dialed number is interpreted to identify a local number in the area code region and in the country in which the subscriber unit is located, rather than a local number in the home area code region or home country of the subscriber. Such eliminates the need of the user to dial long distance area codes or international dialing codes merely to dial a local telephone number. The system is, in another example, configured to identify when an emergency services number, such as 911, is called and to direct the call to the nearest emergency services center to the current location of the subscriber unit. The system also identifies when a call to or from a subscriber unit is subject to law enforcement interception and determines, based upon the location of the subscriber unit, whether the requesting law enforcement agency has jurisdiction to intercept the call.
Although the system of the parent application is effective for parsing or otherwise processing telephone numbers or other telephonic communications based upon the location of the subscriber unit, further improvement would be desirable, particularly in the manner by which the location of subscriber units are tracked in a mobile communications system having multiple service providers.
For example, the mobile communications system may be implemented in accordance with the Global System for Mobile Communications (GSM) protocol. GSM, as it is currently defined, does not support position information other than location area code's (LAC's). LAC's form a portion of a 4-frame broadcast control channel (BCCH) segment of a 51-frame multi-frame signaling structure. Since only four frames are employed to encode the BCCH including the LAC, very little location resolution is accommodated. For a gateway system, which may cover up to 2000 km by 3000 km, the GSM LAC is insufficient to adequately specify the location of a subscriber unit to allow, for example, for a determination of the nearest emergency services station or to allow for a determination of whether a law enforcement agency has proper jurisdiction to intercept calls placed by a subscriber unit located somewhere within the service area. In other words, if the available GSM LAC's were merely equally subdivided over the entire 2000 km by 3000 km service area, each LAC would cover too large an area to be useful for location-based call processing. Hence, there is a need to allow for a greater resolution in location specification within a GSM gateway system and aspects of the invention are drawn to that end.
Even for non-GSM systems wherein location information may be more easily accommodated, different service providers may wish to employ different internal mapping schemes for mapping physical locations of subscriber units into discrete cells. For some service providers, such internal mapping schemes may be based, for example, on conventional cellular telephone system cell layouts as defined by the locations of ground base transceiver stations (BTS's). The layout of such cellular telephone system cells is typically determined or constrained by the physical characteristics of the ground terrain including the location of mountains, buildings, etc. For a satellite mobile transmission system, such physical ground-based limitations are generally irrelevant and "virtual" cells may be defined arbitrarily without regard to the ground terrain.
It is desirable, therefore, to provide a system for mapping physical locations of subscriber units into a variety of different individual service provider cell layouts to accommodate location specification requirements or preferences of different service providers. Even if the various service providers do not have distinct internal mapping schemes and instead can all accept physical location information using a common virtual mapping scheme, the service providers may still prefer or require that communications from the gateway be in a particular unique data format and hence separate service provider cell mappings may be desirable to facilitate the different data formats. Also the different service providers may have different location-based preferences for routing emergency service calls, for intercepting calls on behalf of law enforcement or for encrypting calls.
It is also desirable to provide a system for storing and tracking location-based system information to facilitate access to such information despite the limitations of GSM and the use of different service provider location mapping schemes. Examples of location-based system information include the locations of emergency services centers or any location-based legal or other contractual limitations imposed on service providers to processes calls to or from subscriber units at different locations. In this regard it is particularly desirable to provide a system for tracking such location-based information which allows the information to be updated as needed without affecting any of the individual service provider mapping schemes.
It is to these ends that aspects of the invention of this continuationin-part application are directed.